Is it possible that both embryos implanted and one might continue to develop normally given the decrease in beta-human chorionic gonadotropin (beta-hCG) levels from 204 to 175 over 48 hours after two blastocyst transfers?

Declining β-hCG After Double Blastocyst Transfer: Prognosis and Management

Direct Answer

The declining β-hCG from 204 to 175 over 48 hours (a 14% decline) indicates a failing pregnancy, and it is extremely unlikely that either embryo will continue to develop normally. 1, 2

Understanding the β-hCG Decline Pattern

Your β-hCG pattern shows a 14% decline over 48 hours, which falls far outside the expected range for a viable pregnancy:

• Normal viable pregnancies require a minimum β-hCG rise of 66% over 48 hours 3, 4
• Spontaneous complete abortions show declines of at least 21% at 2 days and 60% at 7 days 2
• Your decline of 14% over 48 hours suggests an incomplete or ongoing pregnancy loss rather than either a viable pregnancy or a complete abortion 2, 4

Why Both Embryos Are Unlikely to Continue

The possibility that one embryo implanted successfully while the other failed does not explain this β-hCG pattern. 1 Here's why:

• If one blastocyst had successfully implanted and was developing normally, the β-hCG should still be rising by at least 66% every 48 hours, even if the other embryo failed 3
• A single viable blastocyst produces sufficient β-hCG to demonstrate appropriate doubling times 3
• The declining pattern indicates that all trophoblastic tissue is failing, not just one embryo 2, 5

Critical Next Steps: Rule Out Ectopic Pregnancy

You must undergo serial β-hCG monitoring combined with ultrasound surveillance to definitively rule out ectopic pregnancy until either an intrauterine pregnancy is confirmed or β-hCG declines to <5 mIU/mL. 1, 6

Specific monitoring protocol:

• Repeat β-hCG in 48-72 hours to confirm continued decline 1, 2
• Transvaginal ultrasound if β-hCG plateaus or fails to decline appropriately 6
• A β-hCG decline of less than 21% at 2 days or 60% at 7 days suggests retained trophoblasts or ectopic pregnancy 2
• Continue monitoring until β-hCG reaches <5 mIU/mL 1

Prognosis and What This Means

Even when cardiac activity is detected on ultrasound, low or inappropriately rising β-hCG levels indicate poor prognosis. 5 In your case:

• The initial β-hCG of 204 on day 12 post-transfer is lower than expected for two implanted blastocysts 5
• The subsequent decline confirms pregnancy failure 2, 5
• All seven pregnancies in one study with positive fetal heart activity but low β-hCG ultimately failed 5

Planning Your Next Cycle

For future IVF attempts, single embryo transfer (eSET) should be your standard approach. 1, 7 The evidence is clear:

• No benefit to double embryo transfer: Cumulative live birth rates with eSET are not inferior to double embryo transfer (DET) 1, 7
• Blastocyst transfers must be single: Blastocysts have higher monozygotic twin potential and significantly increased complication risks when two are transferred 8, 1, 7
• This failed cycle does not change the recommendation: Previous failed treatments do not justify DET in subsequent attempts 1, 7

Risks you avoided by this pregnancy failing:

• 5-fold increase in fetal death with twins 8
• 7-fold increase in neonatal death with twins 8
• 20-fold increased risk of ectopic pregnancy with DET 8
• Maternal complications including pre-eclampsia, gestational diabetes, and emergency cesarean section 8

Common Pitfalls to Avoid

• Do not wait for symptoms before seeking evaluation: Asymptomatic ectopic pregnancies can rupture 6
• Use the same laboratory for serial β-hCG testing: Different assays have varying sensitivities and may detect different HCG isoforms 9
• Do not assume the pregnancy is "complete" until β-hCG reaches <5 mIU/mL: Your current decline rate suggests incomplete abortion 2, 4